Use GetCredentialsForIdentity with an Amazon SDK or CLI

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.cognitoidentity.CognitoIdentityClient;
import software.amazon.awssdk.services.cognitoidentity.model.GetCredentialsForIdentityRequest;
import software.amazon.awssdk.services.cognitoidentity.model.GetCredentialsForIdentityResponse;
import software.amazon.awssdk.services.cognitoidentityprovider.model.CognitoIdentityProviderException;

/**
 * Before running this Java V2 code example, set up your development
 * environment, including your credentials.
 *
 * For more information, see the following documentation topic:
 *
 * https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html
 */
public class GetIdentityCredentials {
    public static void main(String[] args) {

        final String usage = """

                Usage:
                    <identityId>\s

            Where:
                identityId - The Id of an existing identity in the format REGION:GUID.
            """;

        if (args.length != 1) {
            System.out.println(usage);
            System.exit(1);
        }

        String identityId = args[0];
        CognitoIdentityClient cognitoClient = CognitoIdentityClient.builder()
                .region(Region.US_EAST_1)
                .build();

        getCredsForIdentity(cognitoClient, identityId);
        cognitoClient.close();
    }

    public static void getCredsForIdentity(CognitoIdentityClient cognitoClient, String identityId) {
        try {
            GetCredentialsForIdentityRequest getCredentialsForIdentityRequest = GetCredentialsForIdentityRequest
                    .builder()
                    .identityId(identityId)
                    .build();

            GetCredentialsForIdentityResponse response = cognitoClient
                    .getCredentialsForIdentity(getCredentialsForIdentityRequest);
            System.out.println(
                    "Identity ID " + response.identityId() + ", Access key ID " + response.credentials().accessKeyId());

        } catch (CognitoIdentityProviderException e) {
            System.err.println(e.awsErrorDetails().errorMessage());
            System.exit(1);
        }
    }
}